Python Instant Messaging
I looked around to find a simple way of setting up a private instant messaging server, but were unable to find anything easy. Instead, I just made a simple custom solution myself, with a server script and client script written in the Python programming language.
The finished solution turned out to be more like a conference/chat room (IRC with only one channel), but with some features found in instant messaging clients that I think are important. The idea is that there is one server, and then many clients connect to it and everyone will see everything anyone writes.
Here's a screenshot of the graphical Tk-based client:
I have tested the server with Python version 2.5.x and the client with versions 2.5.x and 2.7.x without issues. And since no special libraries are used, it is enough to just download the standard Python distribution, and start using the scripts.
The client and server is available under a MIT License, and can be downloaded here. Unfortunately, there is no documentation, but the scripts should be straightforward to use.